1. Field of the Invention
The present invention relates to a polymer composition for a tire superior in the balance between the resistance to air permeation and the flexibility. More specifically it relates to a polymer composition for a tire which enables the inner liner layer or other layer for prevention of air permeation to be made thinner and the tire to be made lighter, without detracting from the retention of air pressure of the pneumatic tire and also relates to a pneumatic tire using the above-mentioned composition for the air permeation prevention layer.
The present invention further relates to a pneumatic tire having an air permeation prevention layer which is superior in the balance between the resistance to air permeation and the flexibility, which is superior in the attachment and bonding of the inner liner layer or other air permeation prevention layer during the molding and vulcanization of the tire, and which enables the inner liner layer or other air permeation prevention layer to be made thinner and the tire to be made lighter without detracting from the retention of air pressure in the tire.
2. Description of the Related Art
The reduction of fuel consumption is one of the major technical problems to be solved in the automobile industry. There have been increasingly stronger demands for reduction of the weight of the pneumatic tires as part of this approach.
The inner surface of a pneumatic tire is provided with an inner liner layer composed of a low gas-permeable rubber such as butyl rubber or halogenated butyl rubber so as to enable the tire air pressure to be kept constant. A halogenated rubber, however, suffers from a large hysteresis loss. For this reason, when after vulcanization of the tire, there are waves formed in the inner surface rubber of the carcass layer and the inner liner layer in the space between the carcass cords and the inner liner rubber layer deforms along with the deformation of the carcass layer, there is the problem that the rolling resistance increases. Therefore, in general, the inner liner layer (i.e., halogenated butyl rubber) and inner surface rubber of the carcass layer are joined through a rubber sheet, which is called a tie gum having a small hysteresis loss. Accordingly, in addition to the thickness of the inner liner layer of the halogenated butyl rubber, there is added the thickness of the tie gum and the layer as a whole becomes a thickness of over 1 mm (i.e., 1000 xcexcm). As a result, this becomes one factor increasing the weight of the final tire product.
Various proposals have been made for using various materials, in place of the low gas permeable rubber such as butyl rubber, as the inner liner layer of the pneumatic tire. For example, Japanese Examined Patent Publication (Kokoku) No. 47-31761 discloses the coating of the inner surface of a vulcanized tire having a thickness of 0.1 mm or less from a solution or dispersion of a synthetic resin such as polyvinylidene chloride, a saturated polyester resin, or a polyamide resin having an air permeation coefficient (cm3 (standard state)/cmxc2x7secxc2x7cmHg)) of 10xc3x9710xe2x88x9213 or less at 30xc2x0 C. and of 50xc3x9710xe2x88x9213 or less at 70xc2x0 C.
The technique disclosed in this publication is to provide the inner surface of the carcass or the inner surface of the inner liner of a vulcanized tire with a coating of a synthetic resin having a specific air permeation coefficient and making the thickness of the synthetic resin coating of 0.1 mm or less, but the pneumatic tire described in the publication had a problem in the bonding between the rubber and synthetic resin and further had a defect of an inner liner layer inferior in moisture resistance (or water resistance).
Japanese Unexamined Patent Publication (Kokai) No. 5-330307 discloses to halogenate the inner surface of the tire (using a conventionally known chlorination solution, bromine solution, or iodine solution) and form on top of that a polymer coating (thickness of 10 to 200 xcexcm) of methoxymethylated nylon, a copolymer nylon, a blend of polyurethane and polyvinylidene chloride, or a blend of polyurethane and polyvinylidene fluoride.
Further, Japanese Unexamined Patent Publication (Kokai) No. 5-318618 discloses a pneumatic tire having a thin film of methoxymethylated nylon as an inner liner. According to this technique, the inner surface of a green tire is sprayed or coated with a solution or emulsion of methoxymethylated nylon, then the tire is vulcanized or alternatively the inner surface of a vulcanized tire is sprayed or coated with a solution or emulsion of methoxymethylated nylon so as to produce a pneumatic tire. Even in the art disclosed in these publications, however, the water resistances of the thin films are poor and it is difficult to maintain uniformity in film thickness.
Japanese Unexamined Patent Publication (Kokai) No. 6-40207 discloses an example of use of a multilayer film having a low air permeation layer composed of a polyvinylidene chloride film or ethylene-vinyl alcohol copolymer film and a bonding layer comprised of a polyolefin film, aliphatic polyamide film, or polyurethane film as the air permeation prevention layer of the tire. However, in this system, the low air permeation layer lacks flexibility and the film is unable to keep up with expansion and contraction during the use of the tire and therefore cracks.
Further, Japanese Unexamined Patent Publication No. 5-508435 proposes the use, as a tire inner liner composition, of a composition including a halogen-containing copolymer of a C4 to C7 iso-monolefin and p-alkylstyrene plus carbon black, a plasticizer oil, and vulcanization agent as a tire inner liner, but this inner liner has an insufficient air permeation coefficient and is not suitable for reducing the weight of the tire.
As explained above, various materials have been proposed for the inner liner layer of a pneumatic tire, in place of butyl rubber, but none has yet been commercialized. In particular, no material has yet been developed superior in the balance of the resistance to air permeation and flexibility required as an inner liner layer of a pneumatic tire or a material superior in bonding with rubber.
Accordingly, the object of the present invention is to provide a polymer composition for a tire which is optimal for an air permeation prevention layer of a pneumatic tire which enables the tire to be made lighter and which is bondable with a rubber layer, without detracting from the retention of air pressure by the pneumatic tire and a pneumatic tire which constructs an air permeation prevention layer using the same.
Another object of the present invention is to provide a pneumatic tire having an air permeation prevention layer which enables the tire to be reduced in weight and is superior in the resistance to air permeation and the flexibility, without detracting from the retention of air pressure by the pneumatic tire, which may be formed even after the molding of the tire, and which is superior in the self-attachment (bonding) with the superposed films.
In accordance with the first aspect of the present invention, there is provided a polymer composition for a tire having an air permeation coefficient of 25xc3x9710xe2x88x9212 ccxc2x7cm/cm2xc2x7secxc2x7cmHg (at 30xc2x0 C.) or less and a Young""s modulus of 1 to 500 MPa comprising:
(A) at least 10% by weight, based on the weight of the total polymer component, of at least one thermoplastic resin having an air permeation coefficient of 25xc3x9710xe2x88x9212 ccxc2x7cm/cm2xc2x7secxc2x7cmHg (at 30xc2x0 C.) or less and a Young""s modulus of more than 500 MPa and
(B) at least 10% by weight, based on the total weight of the polymer component, of at least one elastomer component having an air permeation coefficient of more than 25xc3x9710xe2x88x9212 ccxc2x7cm/cm2xc2x7secxc2x7cmHg (at 30xc2x0 C.) and a Young""s modulus of not more than 500 MPa, wherein the total amount (A)+(B) of the component (A) and the component (B) is not less than 30% by weight based on the weight of the total polymer component, and a pneumatic tire using this polymer composition for a tire for an air permeation prevention layer.
In accordance with the second aspect of the present invention, there is provided a polymer composition for a tire having an air permeation coefficient of 25xc3x9710xe2x88x9212 ccxc2x7cm/cm2xc2x7secxc2x7cmHg (at 30xc2x0 C.) or less and a Young""s modulus of 1 to 500 MPa comprising:
(A) at least 10% by weight, based on the weight of the total polymer component, of at least one thermoplastic resin having an air permeation coefficient of 25xc3x9710xe2x88x9212 ccxc2x7cm/cm2xc2x7secxc2x7cmHg (at 30xc2x0 C.) or less and a Young""s modulus of more than 500 MPa,
(B) at least 10% by weight, based on the total weight of the polymer component, of at least one elastomer component having an air permeation coefficient of more than 25xc3x9710xe2x88x9212 ccxc2x7cm/cm2xc2x7secxc2x7cmHg (at 30xc2x0 C.) and a Young""s modulus of not more than 500 MPa, wherein the total amount (A)+(B) of the component (A) and the component (B) is not less than 30% by weight based on the weight of the total polymer component, and
(C) in the thermoplastic resin of the component (A), 3 to 70% by weight, based on the total weight of the components (A), (B), and (C), of another thermoplastic resin with a critical surface tension difference of not more than 3 mN/m with the facing rubber layer when used as a tire, and a pneumatic tire using this polymer composition for a tire for an air permeation prevention layer.
In accordance with the third aspect of the invention, there is provided a pneumatic tire using as an air permeation prevention layer a polymer composition for a tire having an air permeation coefficient of 25xc3x9710xe2x88x9212 ccxc2x7cm/cm2xc2x7secxc2x7cmHg (at 30xc2x0 C.) or less and a Young""s modulus of 1 to 500 MPa comprising:
(A) at least 10% by weight, based on the weight of the total polymer component, of at least one thermoplastic resin having an air permeation coefficient of 25xc3x9710xe2x88x9212 ccxc2x7cm/cm2xc2x7secxc2x7cmHg (at 30xc2x0 C.) or less and a Young""s modulus of more than 500 MPa,
(B) at least 10% by weight, based on the total weight of the polymer component, of at least one elastomer component having an air permeation coefficient of more than 25xc3x9710xe2x88x9212 ccxc2x7cm/cm2xc2x7secxc2x7cmHg (at 30xc2x0 C.) and a Young""s modulus of not more than 500 MPa, wherein the total amount (A)+(B) of the component (A) and the component (B) is not less than 30% by weight based on the weight of the total polymer component, and
(D) in the thermoplastic resin of the component (A), 3 to 50% by weight, based on the total weight of the components (A), (B), and (D), of another thermoplastic resin having a melting point not more than the vulcanization temperature, and a pneumatic tire having an air permeation prevention layer obtained by superposing or coating a surface of a thin film of a polymer composition comprised of the components (A) and (B) with another thermoplastic resin (D) having a melting point not more than the vulcanization temperature, followed by vulcanizing.
In accordance with the fourth embodiment of the invention, there is provided a pneumatic tire obtained by superposing or coating between
(i) an air permeation prevention layer having an air permeation coefficient of 25xc3x9710xe2x88x9212 ccxc2x7cm/cm2xc2x7secxc2x7cmHg (at 30xc2x0 C.) or less and a Young""s modulus of 1 to 500 MPa, composed of (A) at least 10% by weight, based on the weight of the total polymer component, of at least one thermoplastic resin having an air permeation coefficient of not more than 25xc3x9710xe2x88x9212 ccxc2x7cm/cm2xc2x7secxc2x7cmHg (at 30xc2x0 C.) and a Young""s modulus of more than 500 MPa and (B) at least 10% by weight, based on the total weight of the polymer component, of at least one elastomer component having an air permeation coefficient of more than 25xc3x9710xe2x88x9212 ccxc2x7cm/cm2xc2x7secxc2x7cmHg (at 30xc2x0 C.) and a Young""s modulus of not more than 500 MPa, wherein the total amount (A)+(B) of the component (A) and the component (B) is not less than 30% by weight based on the weight of the total polymer component, and
(ii) a layer facing at least one surface of the air permeation prevention layer
a layer imparting bondability to the thermoplastic resin and
having a critical surface tension difference between the layer facing the air permeation prevention layer and the bondability imparting layer of not more than 3 mN/m; a pneumatic tire wherein the critical surface tension difference between the air permeation prevention layer and the bondability imparting layer is not more than 3 mN/m; and a process of producing a pneumatic tire comprising the steps of:
superposing or coating between a polymer composition for an air permeation prevention layer having an air permeation coefficient of 25xc3x9710xe2x88x9212 ccxc2x7cm/cm2xc2x7secxc2x7cmHg (at 30xc2x0 C.) or less and a Young""s modulus of 1 to 500 MPa, comprised of (A) at least 10% by weight, based on the weight of the total polymer component, of at least one thermoplastic resin having an air permeation coefficient of 25xc3x9710xe2x88x9212 ccxc2x7cm/cm2xc2x7secxc2x7cmHg (at 30xc2x0 C.) or less and a Young""s modulus of more than 500 MPa and (B) at least 10% by weight, based on the total weight of the polymer component, of at least one elastomer component having an air permeation coefficient of more than 25xc3x9710xe2x88x9212 ccxc2x7cm/cm2xc2x7secxc2x7cmHg (at 30xc2x0 C.) and a Young""s modulus of not more than 500 MPa, wherein the total amount (A)+(B) of the component (A) and the component (B) is not less than 30% by weight based on the weight of the total polymer component, and a layer facing at least one surface of the air permeation prevention layer, a thin film of a thermoplastic resin having a critical surface tension difference with the layer facing the air permeation prevention layer of not more than 3 mN/m, then
processing and vulcanizing the same.